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There’s no question that what you eat influences your health. There is good evidence that the Mediterranean diet – rich in fruit, fish and vegetables, together with olive oil and other unsaturated fats – is associated with longer life expectancies. Elsewhere, researchers postulate that up to 80 per cent of bowel cancers, for example, are related to diet. They recommend a limit to red meat ingestion and an increased vegetable intake to reduce risks of it. The large US Nurse’s Health Study found that women who ate a lot of nuts (not a food known for its low-fat properties) were found to have a lower rate of heart attacks than women who didn’t eat them in the same quantity. In Japan and China, where there is a lower rate of breast cancer, it is thought that this may be related to the high amount of soya in people’s diets.

This week, another claim is made for food. A new book by nutritionist Patrick Holford and journalist Jerome Burne argues that Food is Better Medicine than Drugs. Is it? It is very useful to look at the associations between diet, health and illness. But can foods really be better medicine than medicine itself?

There are many problems with this book. One of them is that it isn’t really about food as medicine. It’s about food supplements. Food supplements are chemicals, just like the chemicals in food, and like typical medicines. However, food supplements are, in the view of the Medicines and Healthcare Regulatory Authority (MHRA), not medicines. Medicines must be licensed for specific conditions and thereafter regulated for quality and adverse effects. Food supplements such as omega-3 oils, ginseng and garlic capsules do not come under the jurisdiction of the MHRA and cannot, therefore, make medicinal claims.

This has not stopped the authors making plenty of claims for food supplements as a replacement for many medicines. They also air the possibility of “100 per cent health”. It is achievable, they say, through a minimum intake of twice-daily, high-strength multivitamins and minerals plus extra vitamin C and omega-3 fats. Apparently, “everyone can benefit from this basic supplementation”. But there is no consensus and certainly no well-designed trial to demonstrate well people getting healthier by taking such supplements.

In the “Helping Your Heart” chapter, people using beta-blocker drugs are told that “there are real concerns about these drugs for anything other than short-term use or for people who have had heart attacks that have resulted in erratic heartbeats due to damage to the heart’s left ventricle”. There is also good-quality clinical research suggesting that people who have had a heart attack, or people who have heart failure, have improved mortality rates using these drugs in the long term.

The side effects – a long list – are nothing new. Certainly these drugs aren’t prescribed for fun. The authors say that you should not stop them suddenly, as “it is better to wean yourself off them”. They don’t, however, discuss their potential advantages, or point out that it is up to the person taking them to make a fully informed decision. For a healthy heart, they recommend instead niacin, mineral-rich foods, B vitamins and omega oils – but no comparative data.

They suggest that aspirin may “unbalance various complex systems in your body, possibly putting you at risk for a number of other problems in the future”. If you have atrial fibrillation, where the atria of the heart do not pump properly, research suggests it may be a good idea to “unbalance various complex systems” as you are at higher risk of having a stroke. There is also evidence that aspirin reduces this risk and that the benefits outweigh the side effects.

Usually, I discuss the pros and cons of such medicines with patients, enabling them to decide if they want to take it. I can’t do this with the book’s recommended fish oils, gingko biloba and garlic – even though the authors claim they are “far more likely to give you a healthy heart” – because, again, there is no comparative evidence for their suggestions. I find this very unhelpful.

If food supplements were better medicine than drugs, I would expect the same level of knowledge about effects and effectiveness before recommending them.

The authors claim that the reason doctors like myself aren’t interested in “nutritional medicine” is partly that we are in thrall to the drug companies and partly that doctors are ignorant and refuse to look at the supportive research. Yet many doctors don’t see drug reps, don’t attend pharma- sponsored “education” events and prefer to rely on impartial evidence instead.

The problem with research is that you should do it to resolve an uncertainty, not to get the result you want and to ignore it when you don’t. The real reason I am not keen on nutritional medicine is that when I look at the evidence, I find that it is oversold. Not unlike this book.